Motors generate twisting reaction forces (reverse torque) which are transmitted to their associated mounting brackets. With reference to hand held power tools, these forces may cause operation of the tool to become inefficient, uncomfortable or even unsafe.
An electric motor consists of an armature and an outside case. The armature is part of the motor's drive shaft and will be referred to herein as the action member. The outside case of the motor is separate from the armature and will be referred to as the reaction member. In prior art configurations, the outside case of the motor is mounted solidly within the tool casing. The armature is caused to turn when electricity is supplied to the motor. The reaction forces are then directly transmitted from the outside case of the motor to the tool casing, where they are contained by the mounting brackets of the tool.
With existing portable hand drills, the hand of the operator is actually the mounting bracket. The reaction forces can be felt by the operator as a twisting effort. The twisting effort (or the reaction force) will be equal to the effort at the drill bit (or the action force).
Planetary gear sets are known to be useful as reduction gear sets and for other power transmission purposes, but have not heretofore been used to eliminate undesirable reaction forces in motor-driven tools.
Prior developments in this field may be generally illustrated by reference to the following patents:
______________________________________ Patent No. Patentee Issue Date ______________________________________ 3,134,275 R. Davison May 26, 1964 2,591,967 H. Ridgely et al. Apr. 08, 1952 1,151,381 N. Olson Aug. 24, 1915 2,826,095 B. Dirzius et al. Mar. 11, 1958 3,204,489 K. Furukawa et al. Sep. 07, 1965 4,901,602 H. Matoba Feb. 20, 1990 2,582,698 E. Hirvonen Jan. 15, 1952 2,899,850 J. Selby et al. Aug. 18, 1959 ______________________________________
U.S. Pat. No. 3,134,275 shows a hand held power tool which utilizes planetary gears to couple the electric motor to the output member. The outside case of the motor 24 of this device is rigidly connected to the tool casing 12. Therefore, the reaction forces of the motor are transmitted to the tool 10 in the traditional manner.
U.S. Pat. Nos. 2,591,967 and 1,151,381 teach other sun gear and planet gear assemblies. Neither teach a configuration which would isolate the reaction forces of a drive motor from an associated power tool.
U.S. Pat. No. 2,826,095 shows a rotating head for a drill which incorporates a planetary gear arrangement. An arm 25 transfers reaction forces or torque (col. 2, lines 3-7) from the planetary gear set to the tool (in this case a drill press 12) rather than isolating them from the tool.
The rest of the patents are representative of what is in the art.